In conventional housing technology of chips, e.g. semiconductor chips, a chip may be bonded to a carrier, e.g. a leadframe. Requirements regarding a thermal and/or an electrical conductivity of the leadframe may lead to copper (Cu) as a material of choice for the leadframe. The thermal and electrical conductivity of copper may be comparatively high.
Typically, the bonding of the chip, e.g. the semiconductor chip, to the leadframe may be formed at an elevated temperature, for example a temperature of more than 200° C. Since coefficients of thermal expansion (CTE) of the bonding partners, i.e. of the chip and the carrier, e.g. the leadframe, may be different, a cooling of the bonded system (of the chip bonded to the leadframe) may lead to a relatively high stress.
The stress may lead to a change in electrical properties of semiconductors, e.g. of the semiconductor material of the chip, and/or to a mechanical failure, for example during a stress test.
A similar kind of stress may be caused by contacting the chip with clips, or by plating, e.g. electroplating, metal contacts on the chip, even though an amount of stress may be lower.
Also in a case where a low-temperature bonding method may be used, e.g. a bonding at room temperature, thermal stress may be caused during an operation of the chip, because operation temperatures, e.g. of power chips, may reach temperatures as high as about 260° C.
In other words, when a device including a semiconductor, e.g. a chip, having a material, e.g. a metal, with a CTE significantly different from the CTE of the semiconductor formed on it, is subjected to large temperature changes, stress may be induced in the semiconductor and/or a connection between the semiconductor and the material (e.g. the metal), irrespective of whether the temperature change may be caused by a cooling after a high-temperature bonding of the material to the semiconductor, a heating of the device during operation, a heating/cooling of the semiconductor device due to ambient temperatures at its place of operation, or any other temperature change.
Until today, a solution for lowering the severe, temperature-induced mechanical degradation of devices and/or of stress between the semiconductor, e.g. silicon, and a metal, e.g. copper, wherein at the same time avoiding a significant influence on (e.g. degradation of) the thermal and/or electrical conductivity of the system, has not been found.